State of The Art
It is already known to use the CAN system in connection with vehicles and mobile equipment. From the publication dated 30-03-1994 from Honeywell Micro Switch Division, it is known to provide a special program in the system in order, after restarting in the system, to make the various modules work with a bit speed fixed by or in the system. Among other things, a special NOOP message is transmitted on the bus connection upon restarting. A special elimination bit in this connection is initiated in a control register in the system, which causes the transmitter in question to terminate its message, irrespective of whether acknowledgement is received or not. The master module must subsequently check whether there is a NOOP acknowledgement on the connection. If no such acknowledgement appears on the connection, the master module repeats the check. If the acknowledgement exists, the module takes this as confirmation that the connection is in operation, whereupon other nodes can adjust themselves to the correct bit speed or corresponding parameters.
It is possible, in a conventional manner, to prevent the CAN circuit from carrying out transmission on the bus connection in association with the restarting. This can take place, e.g., by the output in question from the CAN circuit being programmed to make this possible. In this manner, the CAN circuit can be made to listen to the bus without the CAN circuit transmitting an error message or acknowledgement bit on the bus connection in question. When the CAN circuit receives a message, this takes place at a bit speed which can be set with certain parameters and which can be adjusted to make possible reception of the bit speed applicable in the system. In this manner, the CAN circuit can communicate on the connection without disrupting or corrupting the communication on the connection by working with incorrect parameters/bit speed. It is to be noted in this case that the rules of the CAN system state that one priority field in the CAN system may not be used by two modules simultaneously. In order to avoid an error message if two or more modules are transmitting simultaneously, this must be counteracted with the aid of rules in the software and programs of the CAN system (cf. above).